Generally, as shown in FIG. 1, the image compression method recommended by JPEG is carrried out after performing a discrete cosine transformation (DCT) conversion in order to carry out data compression within a digital image recording and reproducing device. Here, a quantizing step size is determined by a certain scaling factor S of a quantizing matrix which consists of 8.times.8 blocks, and in which the human optical characteristics are taken into account. Even if the quantizing step size is decided based on the certain scaling factor S, a sophisticated image can not be reproduced accurately and even a simple image requires a large amount of memories in its processing.